1. Field of the Invention
The present invention relates to an image stabilizing device for preventing image blur caused by shaking of an optical system, and more particularly to an image stabilizing device capable of properly responding to various operations in a camera.
2. Related Background Art
There have been proposed various control devices for image stabilization, or for preventing image blur caused by shaking of the camera. Such a device is generally constructed as a feedback control mechanism for controlling a lens system in such a manner as to suppress the displacement of the image caused by radial shaking of the lens system.
For example, the vibration of a camera (usually vibration in a direction inclined to the optical axis of photographing) is detected as an acceleration signal, which is integrated in a signal processing system to obtain a displacement signal or a velocity signal, and such signal is used for driving the lens system in a direction to suppress the vibration.
In case of single-lens reflex cameras, such device is either incorporated in an interchangeable lens, or formed as an adaptor to be inserted between the camera body and the lens.
FIG. 6 shows an example of the control unit of an image stabilizing device with a conventional signal processing system, wherein an acceleration detector 101 detects the inclination of a camera (not shown) with respect to the optical axis, as an acceleration signal. The acceleration signal a is integrated by a first integrator 102 into a velocity signal v, which is further converted by a second integrator 103 into a displacement signal d. An actuator 105 moves, according to the displacement signal d, an imaging system 104 of the camera, said system 104 being radially movable in order to prevent image blur.
A variable resistor 106 constitutes position detecting means for detecting the actual displacement of the imaging system 104. The signal from the position detecting means is fed back to the input system of said actuator 105. In this manner there is formed a local feedback loop for controlling the imaging system 104 in correspondence with the displacement caused by vibration. An operational amplifier 107 is provided between the integrator 103 and the actuator 105. A spring 108 biases the imaging system 104 to an end of the movable stroke thereof when the actuator 105 is not energized. Thus, the radial position of the imaging system 104 is determined by the balance between the force generated by the actuator 105 and the force of the spring 108. The position of the imaging system 104 at the center of the movable stroke therein is represented by l/2 measured from the position of the imaging system 104 when the actuator 105 is not energized, wherein l represents the entire radial stroke of the imaging system 104.
When the actuator 105 is energized, the image stabilizing device starts its function from a state in which the imaging system 104 is positioned at the end of the stroke closest to the actuator 105. Thus, the imaging system 104 cannot be moved further toward the actuator 105, so that satisfactory image stabilization cannot be expected. Therefore, in order to prevent such phenomenon and to secure strokes for the imaging system 104 in both radial directions, there is required a centering operation for moving the imaging system 104 to the central position (l/2) of the stroke when the actuator 105 is energized, and the image stabilizing operation is initiated after said centering.
Also, since the stroke of the actuator 105 is limited, the imaging system 104 may be brought to an end thereof in response to a very large vibration. If the shutter of the camera is released in such state, there cannot be expected satisfactorY image stabilization, and image blur will be observed in the resulting photograph. In order to prevent such phenomenon, it is necessary to conduct the centering operation prior to the release of the shutter, in order to secure the strokes of the imaging system
However, such image stabilizing device is usually incorporated in the interchangeable lens, or formed as an adaptor to be positioned between the camera body and the lens as explained before, and is designed to effect the image stabilization or the centering independent from the operations in the camera body. For this reason such device has been associated with drawbacks, such as inability to properly respond when the image stabilizing operation or centering operation is required in the camera body, for example, at the start of operation therein, or at the release of the shutter, or a wasted operation of the device resulting in the consumption of battery when the image stabilization is not required by the camera.